Diet and fitness: Fancy some fresh-air?

You might either cry or sigh with relief to hear that the gym is dying. According to a report published by Deloitte last week, membership figures have plummeted from a record high five years ago, when 8.7 million of us were signed up.

Last year, however, card-carrying membership dipped by up to eight per cent in some parts of the country - notably the West Midlands, the North-East and Northern Ireland.

For once, it's not easy to write off this decline as further evidence of the credit crunch forcing cash-strapped Britons to slash their monthly bills - joining fees have also dropped, down an average 17 per cent. It seems we have just fallen out of love with the gym. We all want to keep fit, but not in a sweat-soaked basement surrounded by people in ill-fitting Lycra.

Even the lightest of exercise is better for you when conducted outdoors; studies show that negative ions in fresh air generate increased alertness and elevate your mood. Also, outdoor exercise burns more calories than equivalent activities in a gym, especially when there's a chill-factor involved - the body can use up to 50 per cent more calories just to keep warm. Jogging around a park - with the changes in incline, stride length, and various twisting and turning movements required on uneven and unfamiliar terrain - will also tone up a greater number of muscle groups than a running machine.

And with spring just around the corner, bringing with it a winning combination of fresh air and sunlight - you need 15 minutes of rays to get your recommended dose of vitamin D - you're more likely to keep up your regime.

I found an outdoor fitness course operated by my local gym, of all places. Erik Solang, a super-fit Swedish fitness instructor at Virgin Active in Islington, north London, runs a new "fresh-air fitness" programme called Outdoor Active. Essentially, it's circuit training out in the open, with a range of different exercises performed in short bursts, "on the whistle", sergeant major-style.

As the class of four leaves the gym for a small public garden across the road, Erik explains that he likes to think of this programme as "boot camp with a smile". That I might look a bit of a berk doing forward lunges, 10m sprints and press-ups on kettleballs (it works the chest and shoulder muscles harder) is by-the-by. No shame, no gain. I'm soon grunting and groaning like Johnny Vegas playing squash, but Erik's having none of it. "Come on! You can do better than that!"

In truth, it's good to have someone giving you a gentle kick up the backside. It's easy not to push yourself when you're on your own in a gym, but in a group and with an instructor nudging you onwards, you're more likely to give it that extra 10 per cent.

According to Dr David Haslam, clinical director of the National Obesity Forum, the key to a successful exercise programme is sustainability. "If you're just running on a treadmill getting bored, you're less likely to keep it up. If you're in a more pleasant environment, perhaps with a social element as well, you'll be more inclined to make a habit of it."

There's also a lot to be said for "getting out there", whatever the weather. Running around a park requires a different spatial awareness than a session on a treadmill. And there's good news for men: more testosterone is released by the body in the colder months, which means you can build and tone muscles more easily.

As I stagger around the gardens carrying a 5kg weight on my shoulders, I feel a strange throb in my biceps, calves and hamstrings, as if they've just been woken from a long slumber.

By the end of the session, I'm aching, but I'm also alert and buzzing, as nature intended. When I step back into the gym to get changed, my newly cleansed nostrils get a whiff of the cardio room. Poor gym rats, I think. They don't know what they're missing.

THE GREAT OUTDOORS

Jog around Princes Street Gardens, Edinburgh 10 minutes, burns 100-150 calories Once around the fountain- and statue-filled parkland in the shadow of Edinburgh Castle is just under a mile.

Swim two lengths of the Serpentine lido in Hyde Park 15 minutes, burns 100 calories In the summer months, the lake in London's most famous park is a fantastic place to swim. At just over 100 metres in length, a swim back and forth will expend enough energy to earn coffee and cake in the waterside cafe.

Walking the dog along Brighton Beach 20 minutes, burns 100-150 calories At an average pace, the 1.5-mile stroll from the pier to the marina will burn off more than 100 calories, depending on body mass. If you walk on the pebbles, you'll expend even more energy, and give your calves and hamstrings a tougher workout.

Climbing up Solsbury Hill 30 minutes, burns 400+ calories It's a steep climb from Batheaston to the summit of the Somerset hill immortalised in Peter Gabriel's song. The view over Bath makes it worthwhile.

Cycle the Phoenix Trail 60 minutes, burns 350+ calories Repurposed for walkers, in-line skaters and horse-riders, this flat, six-mile stretch of disused railway line between Thame in Oxfordshire and Princes Risborough in neighbouring Bucks also makes for a genteel Sunday afternoon ride. Burn copious calories as you pass through open country and admire the outdoor sculptures dotted along the route.